My invention comprises improvements in a residential heat pump system of the kind shown, for example, in U.S. Pat. No. 5,029,449, which is assigned to the assignee of my invention. It is an improvement also in the heat recovery method described in U.S. Pat. No. 4,510,762, which is assigned to H. Krantz, GmbH and Company of Germany.
The heat pump system of the '449 patent includes an outdoor unit and an indoor unit. The outdoor unit comprises an engine of the internal combustion type which drives a compressor. It includes also an outdoor refrigerant coil that receives the output of the compressor as a part of a refrigerant circuit. The controls include a thermal expansion valve and a fan powered by an electric motor for circulating ambient air across the outdoor coil.
The refrigeration and heat pump system uses ambient outside air as a heat sink for the cooling move and as a heat source when the system is operating in the heat pumping mode.
A residential heat pump that uses a gas engine to drive the compressor for the refrigerant may have an exhaust system that will recover waste heat from the exhaust and reduce exhaust noise to an acceptable level. Further, the exhaust system must either minimize condensation in the exhaust gases or properly dispose of the condensate if condensate is formed. Discharge of heat and odor from the exhaust should occur at a location that does not create an objectionable environment.
Exhaust noise from an engine-driven heat pump can be mitigated by a conventional muffler, but mufflers typically do not reduce the intensity of the noise to an acceptable level for most residential heat pump installations unless they are of a size that would make them impractical. Further, a typical muffler will not eliminate the distinctive noise signature (i.e., noise pulses) that are typical of a single cylinder gas engine heat pump.
If the outdoor coil is used with an outdoor fan that is driven by an electric motor, the fan noise can be used to mask engine exhaust noise to a certain extent, but the outdoor fan itself is somewhat noisy. If the fan were to be at a location that is not proximate to the exhaust, the engine exhaust noise may be a source of noise that is distinguishable from the background noise of the fan itself.
Condensation of water vapor in the engine exhaust also creates a concern. The exhaust condensate can be a source of heat if there were a practical means to extract it as is done in condensing furnaces. The outdoor location of the condensate, however makes disposal much more difficult than for a typical residential basement furnace. If a significant quantity of condensate is collected and disposed of outdoors during freezing weather, a large quantity of ice may be formed, which would be unacceptable. The condensate also is mildly acidic, and care must be taken to prevent corrosion of the heat pump housing and adjacent structural parts of the heat pump system.
In the past, it is known to provide engine exhaust outlet configurations for a gas engine heat pump wherein the exhaust gas discharge is mounted low on the outdoor cabinet or housing. This avoids direct corrosion of the heat pump from the moisture in the exhaust. Prevailing winds, however, may blow the exhaust back onto the cabinet, or the outdoor fan may draw exhaust through the heat exchanger. In cold weather, condensation may result which may create a corrosion problem. Further, condensation of water vapor on the refrigerant coil may occur. This may decrease performance and make it necessary to employ a defrost cycle more frequently. Also, the concentrated exhaust at ground level is a localized source of noise and odor that is Particularly noticeable to the persons near the residence.
Other known heat pump arrangements route the engine exhaust stream vertically downward across the face of the outdoor heat exchanger. The exhaust is drawn through the heat exchanger by the outdoor fan. Although the noise and odor are less objectionable with this arrangement, long-term corrosion of the heat exchanger and the associated parts presents a problem.
One design approach involves discharging the exhaust gases into the cavity between the outdoor heat exchange and the outdoor fan. This may mask the noise and odor since the exhaust gases enter the outdoor fan flow. It also may eliminate some of the corrosion concerns since the exhaust joins the airflow downstream of the heat exchanger. The cold air from the heat exchanger, however, may cause frosting of the fan and the protective grill. This may lead to corrosion of the parts, fan imbalance, and reduced airflow.